A threat of ultraviolet rays (UV-rays) accompanying formation and development of the ozone hole, in particular, a fear of skin cancer caused by irradiation with UV-rays is a threat and fear not only to people in the southern hemisphere, in which the development of the ozone hole is significant, but to all mankind, and measures against UV-rays are a big problem.
Meanwhile, brown suntan is still a determinant of health and attractiveness, and young people are often eager to bask in the sun.
Further, in terms of maintaining health, there is a need to acquire vitamin D through exposure to the sunlight.
From the above-mentioned points, it is strongly desired to bask in the sunlight while avoiding UV-rays (UV-A: wavelength of from 315 nm to 380 nm, UV-B: wavelength of from 280 nm to 315 nm, and UV-C: wavelength of from 200 nm to 280 nm or less), which are harmful to a human body.
In daily life, measures to avoid suntan (measures against UV-rays), which are taken in reality, include using goods, such as a hat, long gloves, and a parasol, wearing a long-sleeved shirt or the like, and applying cosmetics or drugs for avoiding suntan to exposed skin.
However, even though an amount of UV-rays in the sunlight is large not only in the heat of midsummer but also in cloudy days, the measures against UV-rays often tend to be neglected in cloudy days. Further, when it suddenly changes to a weather with a large amount of UV-rays while out of the house, the measures against UV-rays often cannot be taken securely.
In view of the above, there have recently been started to be proposed or commercialized a mobile ultraviolet light sensor so as to measure UV-rays and take appropriate measures against UV-rays.
Incidentally, the sunlight includes visible light and infrared light in addition to UV-rays. Therefore, when an irradiation amount of UV-rays is to be measured, a correct irradiation amount of UV-rays cannot be measured unless the influence of rays other than UV-rays on a measured value is avoided.
When bulk silicon (Si) is used as a semiconductor substrate, a silicon (Si) layer is sensitive not only to UV-rays but also to visible light and infrared light. Therefore, for example, an optical filter for cutting visible light and infrared light is necessary, and has caused an increase in cost. As one solution to the problem, there are examples in which a thin-film silicon-on-insulator (SOI) substrate is used (Non Patent Documents 1 and 2).
The UV sensor disclosed in each of Non Patent Documents 1 and 2 is selectively given high sensitivity mainly to light having a wavelength of 400 nm or less utilizing the fact that the SOI layer is thin and relatively easy to transmit visible light and infrared light.